Conventionally, a light-emitting element such as a Light Emitting Diode (hereinafter, referred to as LED) is used as a light source of a backlight for irradiating a display panel, such as a liquid crystal display panel, from a side of the display panel. Light-emitting elements adopting various arrangements have been proposed so that light emitted from the LED is efficiently taken out from the light-emitting elements.
For example, FIGS. 10(a) and 10(b) illustrates a light-emitting element disclosed in Japanese Unexamined Patent Application Publication No. 2004-282004 (published on Oct. 7, 2004) (Publicly Known Document 1).
FIG. 10(a) is a plan view illustrating a conventional light-emitting element, and FIG. 10(b) is a cross-section view taken along the line I-I in FIG. 10(a).
As illustrated in FIGS. 10(a) and 10(b), the conventional light-emitting element includes an LED 501, a first electrode 503 formed on a substrate 505, a second electrode 504 formed so as to be away from the first electrode 503, and a light reflecting metal body 502 for reflecting light emitted from the LED 501.
The light reflecting metal body 502 has a light reflecting plane 502a, which is formed by etching around a position where the LED 501 is to be provided, and also is stacked integrally with the substrate 505. Further, translucent resin such as a translucent resin lens 506 is provided so that an outer circumferential rim of its convex plane is located at a top rim of the light reflecting plane 502a of the light reflecting metal body 502. This causes a surface on which the LED 501 is mounted is coated with the translucent resin lens 506.
Note that the light reflecting metal body 502 is preferable arranged to efficiently emit the light emitted from a light-emitting plane of the LED 501, via the translucent resin lens 506. The following description deals with how to form the light reflecting metal body 502 in a method for manufacturing this conventional light-emitting element.
FIG. 11 (a) illustrates a state, in a step for manufacturing the conventional light-emitting element, where the light reflecting metal body 502 has been not formed yet. FIG. 11(b) illustrates a state, in the step for manufacturing the conventional light-emitting element, where the light reflecting metal body 502 has been already formed.
As illustrated in FIG. 11(a), a mask layer 511 is formed on a metal layer 512 such that at least a region where the LED 501 is to be provided is opened. Thereafter, as illustrated in FIG. 11(b), the light reflecting plane 502a is formed by selectively etching the metal layer 512. At this point, a shape of the light reflecting plane 502a is controlled by adjusting an etching level, so as to have a curved surface. This allows the light to be efficiently reflected from the side surface of the light reflecting metal body 502.
Meanwhile, the method for manufacturing the light reflecting metal body 502 is also applied to a method for manufacturing other components. For example, Japanese Unexamined Patent Application Publication No. 2005-167086 (published on Jun. 23, 2005) (Publicly Known Document 2) discloses an arrangement in which, by using a method similar to the aforementioned method, a convex metal portion is formed on an LED mounting substrate.
FIG. 12 is a cross-section view illustrating a conventional LED mounting substrate.
The conventional LED mounting substrate, as illustrated in FIG. 12, includes a convex metal portion 603 formed in a region where an LED 601 is to be mounted via a heat radiating pattern 602b. With this arrangement, heat created at the LED 601 is led to a metal substrate 604 via the heat radiating pattern 602b and the convex metal portion 603. This improves a heat radiation effect. Further, the LED 601 is electrically connected with an electrode section 602a, and a light reflecting body 605 is formed on a surface of the electrode section 602a so as to surround the LED 601.
As in the aforementioned method, the convex metal portion 603 is formed by (i) forming a metal layer on a metal substrate 604, (ii) forming an etching resist on a surface of the metal layer, and then (iii) etching the surface of the metal layer selectively.
Meanwhile, the light-emitting element, including a light reflecting surface formed by carrying out wet etching with respect to a metal plate, is not manufactured individually. Instead, a plurality of light-emitting elements are arranged at a prescribed interval and simultaneously manufactured in a single metal plate, and ultimately cut with a blade (a cutter) into light-emitting elements, individually.
FIG. 13(a) is a cross-section view illustrating the light-emitting element that has not been cut into light-emitting elements individually, as viewed from a side surface along a short side thereof. FIG. 13(b) is a plan view illustrating a state where a mask member 705 is detached from the light-emitting element of FIG. 13(a). FIG. 13(c) is a plan view illustrating a state where the mask member 705 is attached to the light-emitting element of FIG. 13(a). Additionally, only the two light-emitting elements are illustrated in FIGS. 13(a) to 13(c) for convenience.
The light-emitting element illustrated in FIGS. 13(a) to 13(c) includes a Cu wiring layer 701, a resin layer 702, an etch stop layer 703, a light reflecting metal wall 704 having a light reflecting surface 704a, and a mask member 705 which is made of metal. In such a light-emitting element, it is necessary to form the light reflecting plane 704a by carrying out wet etching with respect to the metal plate under three conditions described below.
Condition A
An LED chip mounting surface 706 should be made flat and wide.
Condition B
A thickness B of the light reflecting metal wall 704 should be made as thick as possible, the thickness B being in a direction parallel to the LED chip mounting surface 706.
Condition C
A height C of the light reflecting metal wall 704 should be higher than a desired height, the height C being in a direction perpendicular to the LED chip mounting surface 706.
The following describes CONDITION A. In a case where the LED chip is provided and is subjected to a conductive connection by wire bonding, there is a need to secure an area for industrial tools. Therefore, on the LED chip mounting surface 706, a minimum required width A needs to be secured and widened. Further, the LED chip mounting surface 706 needs to be flat so that the LED chip is suitably mounted.
The following describes the CONDITION B. By cutting a part with a blade, the part indicated by an arrow X, the light-emitting elements is prepared individually. Therefore, when the light reflecting metal wall 704 has a thin thickness B, there is a possibility that the light reflecting metal wall 704 is damaged during the cutting. Further, in cases where the light-emitting element is the one obtained by being individually cut, when the light reflecting metal wall 704 has a thin thickness t, this also causes some problem in view of an end product. As such, the thickness B of the light reflecting metal wall 704 needs to be made as thick as possible by taking into consideration a width P of the blade used in the cutting.
The following further describes the CONDITION C with reference to FIGS. 14(a) and 14(b). FIGS. 14(a) and 14(b) are diagrams explaining the height C of the light reflecting metal wall 704.
As illustrated in FIGS. 14(a) and 14(b), the light-emitting element has an arrangement in which sealing resin 709 is filled in an inner circumferential space, where the light reflecting surface 704a of the light reflecting metal wall 704 is formed, so that an exposed surface of the sealing resin 709 and the top surface of the light reflecting metal wall 704 form a single surface. This causes the sealing resin 709 to cover an LED chip 707 and a wiring 708. Thus, an area in which the sealing resin 709 is provided is determined in accordance with the height C of the light reflecting metal wall 704. As a result, it is necessary to determine the height C of the light reflecting metal wall 704 in accordance with a positional relationship causing the LED chip 707 and the wiring 708 not to protrude from the sealing resin 709.
Further, in a case where the light reflecting metal wall 704 has a low height C as illustrated in FIG. 14(a), a directivity angle α (an angle at which the light emits) becomes wider than a case where the light reflecting metal wall 704 has a high height C as illustrated in FIG. 14(b). It is not preferable to make the directivity angle α too wide, because if the directivity angle α is wide, then loss of light will increase. As such, it is necessary to set the height C of the light reflecting metal wall 704 to be higher than a desired height, by taking into consideration (i) the positional relationship causing the LED chip 707 and the wiring 708 not to protrude from the sealing resin 709 and (ii) the setting of the directivity angle α.
It is desirable to meet the aforementioned three conditions. However, as described in Public Known Documents 1 and 2, according to the conventional method, the metal plate is protected with the mask member and wet etching is carried out with respect to the metal plate. It is difficult to form a required shape of the opening portion of the light reflecting surface, because metal is a material which is etched isotropically.
For example, as illustrated in FIG. 15, it is assumed that the height C of the light reflecting metal wall 704 (a distance from the etch stop layer 703 to the opening portion) is set to be longer than a lateral width W of a packaged light-emitting element. In this case, since etching is performed isotropically, the etching is carried out up to an area of the LED chip mounting surface in a lateral direction of the opening portion but the etching is not carried out up to the etch stop layer 703 in a height direction of the opening portion (see an arrow Z).
On the contrary, it is assumed that the height C of the light reflecting metal wall 704 is set to be shorter than the lateral width W of the packaged light-emitting element. In this case, the etching is carried out up to the etch end layer 703 in the height direction of the opening portion but the etching is not carried out enough in a lateral direction of the opening portion. As a result, the light reflecting surface 704a has a shape causing a vicinity of the LED chip mounting surface to rise in a curved manner. This causes the area of the LED chip mounting not to be secured sufficiently.
It is possible to further carry out the etching because the etch end layer 703 is formed on a surface that is to be the LED chip mounting surface. However, an opening width of the light reflecting metal wall 704 becomes wider than necessary in the vicinity of the mask member 705, and the thickness of the light reflecting metal wall 704 becomes too thin in the vicinity of the mask member 705. This arises a problem that a shape of the light reflecting metal wall 704 can not be kept due to lack of strength.
For the aforementioned reasons, in order that (i) the area of the LED chip mounting surface and (ii) the thickness B of the light reflecting metal wall 704 are both secured while the height C of the light reflecting metal wall 704 is kept at a desired required height, the only way is to increase the size of a light-emitting element, in particular, the lateral width W of the short side of the packaged light-emitting element.